Static multicast filters

This filter type enables the switch to forward or drop multicast traffic to a specific set of destination ports. This helps to preserve bandwidth by reducing multicast traffic on ports where it is unnecessary, and to isolate multicast traffic to enhance security.

You can configure up to 16 static multicast filters (defined by the filter command). However, if an IGMP-controlled filter for a joined multicast group has the same multicast address as a static multicast filter configured on a given port, the IGMP-controlled filter overrides the static multicast filter configured on that port. Note that in the default configuration, IGMP is disabled on VLANs configured in the switch. To enable IGMP on a specific VLAN, use the vlan <vid> ip igmp command. (For more on this command, see “Multimedia Traffic Control with IP Multicast (IGMP)” in the multicast and routing guide for your switch.)

The total of static multicast filters and IGMP multicast filters together can range from 389 to 420, depending on the current max-vlans setting in the switch. If multiple VLANs are configured, then each filter is counted once per VLAN in which it is used.

Multicast filer limits

Max-VLANs setting

Max # multicast filters (static and IGMP combined)

1 (minimum)

420

8 (default)

413

32 or higher

389

Per-Port IP Multicast Filters

The static multicast filters described in this section filter traffic having a multicast address you specify. To filter all multicast traffic on a per-VLAN basis, see “Configuring and Displaying IGMP” in the multicast and routing guide for your switch.

IP Multicast Filters

Multicast filters are configured using the Ethernet format for the multicast address. IP multicast addresses occur in the range of 224.0.0.0 through 239.255.255.255 (which corresponds to the Ethernet multicast address range of 01005e-000000 through 01005e-7fffff). Any static Traffic/ Security filters configured with a multicast filter type and a multicast address in this range will continue to be in effect unless IGMP learns of a multicast group destination in this range. In this case, IGMP takes over the filtering function for the multicast destination address(es) for as long as the IGMP group is active. If the IGMP group subsequently deactivates, the static filter resumes control over traffic to the multicast address.

CAUTION:

If Spanning Tree is enabled, then the MSTP multicast MAC address (0180c2- 000000) should not be filtered. (STP will not operate properly if the MSTP multicast MAC address is filtered.)